The present invention relates to an apparatus and method for the recovery and purification of water from the exhaust gases of internal combustion engines, such as those used in land transit vehicles, (e.g., cars). More particularly, an on-board, portable device produces potable water from vehicle exhaust gases.
Several devices have been utilized over the years to attempt to provide a feasible system for producing potable water from vehicle engine exhaust. These attempts have been generally unsuccessful.
Combustion of diesel, kerosene, gasoline, LP gas or other fossil fuels in an internal combustion engine produce water vapor, which is expelled with the exhaust gases. The present invention allows for the recovery of that water to provide a source of water for potable and other uses. The engine exhaust emissions vary as a function of fuel type and composition, as well as the fuel:air ratio, the type of engine and mode of its operation, and also factors such as ignition timing, cylinder design and fuel additives. Although the relative concentrations of various exhaust components may change depending on the mode of engine operation, generally the nature and content of exhaust remains within a predictable range. It would be useful to be able to capture this water vapor and turn it into drinkable water, particularly for military operations or travel in hostile environments (e.g., desert areas).
The concentration of water vapor in exhaust gases of either gasoline or diesel engines or turbines ranges up to about 10% by volume. Upon cooling the exhaust gases below its dew point, i.e. about 100xc2x0 F., water begins to condense. Some gases present in the exhaust, such as oxygen, nitrogen and hydrogen, do not condense. The other exhaust components, such as hydrocarbons, sulfur dioxide, nitrogen oxides, carbon dioxide and particulates and suspended solid matter, other dissolved organic and inorganic matter (including metals), contaminate the condensed water by dissolving in or condensing with the water vapor and must be removed to obtain a potable water product. The treatment apparatus for the recovery of potable water from the engine exhaust must condense the water vapor, remove the particulates, and purify the water produced therefrom.
Vehicle exhaust gases and the condensed water produced therefrom are very corrosive. The untreated water that is recovered from the exhaust has a pH of about 3 and, in combination with high temperatures, corrosion easily occurs in pits and crevices of a heat exchanger, ducting and ancillary equipment used to condense it. High exhaust temperatures and the elevated ambient temperatures that prevail under desert/arid conditions exacerbate the rates of chemical attack on materials. Hence, the selection of materials for the components is extremely important.
Attempts to recover drinking water from exhaust gases of vehicles have heretofore been unsuccessful because the purification of the water was not considered technically and commercially feasible (i.e., the apparatus was too large, the impurities were too high and/or the process was too expensive).
In brief, the present invention relates to a method for recovering potable water from the exhaust gases of an internal combustion engine, comprising the steps of:
(a) cooling said exhaust gases so as to cause water to condense from said gases (for example, utilizing heat exchangers);
(b) passing said water through one or more particulate filters having a maximum pore size of from about 0.1 to about 10 microns;
(c) passing said water through one or more activated carbon beds (a preferred one sequentially combining a wood-based carbon having a majority of pores in the range of from about 17 to about 40 xc3x85, with a coal-based water-treatment carbon having an average pore size of from about 6 to about 20 xc3x85xe2x80x94the wood-based carbon preferably made by phosphoric acid activation and treated to minimize the amount of phosphorous released into the water); and
(d) passing said water through one or more ion exchange resin beds (a preferred one being a mixed bed of highly acidic and strongly basic type 1 ion exchange resins with low organics and particulate contaminants with high cation and anion exchange capacity).
Optionally, a buffer such as sodium bicarbonate or a base such as sodium hydroxide may be added to decrease water acidity. The sodium bicarbonate may also improve the taste of the water. These additions may be carried out before either the carbon filtration or the ion exchange resin filtration steps.
This system can provide potable water having TOC less than about 0.5 ppm, an inorganic content less than about 2 ppm, and a pH between about 6 and about 8. The potable water can be produced at a rate of at least about 0.5 gallons of water per gallon of engine fuel combusted.
The present invention also includes an apparatus for recovering potable water from the exhaust gases of an internal combustion engine comprising a means for connecting said apparatus to the exhaust portal of said engine (preferably via the catalytic converter); a means for cooling the exhaust gases so as to cause the water in said gases to condense; a means for collecting said water and channeling it to a purification system which comprises one or more particulate filters having a maximum pore size of from about 0.1 to about 10 microns, one or more activated carbon beds, and one or more ion exchange resin beds; and means for collecting the water which has passed through said purification system.
More specifically, this invention relates to a portable apparatus and the method of recovery and purification of potable water from vehicle exhaust gases. Water can be produced at a rate of at least about 0.5 gallons/gallon of diesel using a 6.5 liter diesel engine with a compression ratio of 21:5:1 and a Brake Mean Effective Pressure (BMEP) of about 300 psi, as is standard issue in a HUMVEE, or xe2x80x9cHMMWVxe2x80x9d United States armed forces vehicle, while having only a small (i.e.  less than 7%) effect upon the engine performance of the vehicle. A combination of particulate filtration to remove solids, treatment by activated carbon to remove organic compounds and some inorganics, and treatment by ion exchange resin to remove ionic species, provide effective removal of toxic and other contaminants to produce potable water having a purity which exceeds the EPA drinking water standards, as well as the DOD TB MED 577 tri-service water quality standards for long-term consumption.
The activated carbon material used in the instant invention removes essentially all of the organic contaminants, even though some are present at concentrations in the ppb range. The water purification step involves passing the water condensed from the exhaust gases having a high concentration of Total Organic Carbon (TOC) materials of from about 50 to about 250 mg/L and a pH of about 2.8, through a particle filter and an activated carbon filter to obtain TOC levels in a range of from about 3 to about 100 mg/L. The resulting product is then passed through an ion exchange resin to remove metals, inorganic, acidic, and remaining organic contaminants. The filtered water samples have a TOC content below detectable limits (BDL) which is 0.5 mg/L for current EPA drinking water regulations and as low as 0.1 mg/L in some instances. This is a significantly lower TOC than a control sample obtained from the local municipal water supply (2.6 mg/L). Moreover, the filtered samples did not contain any of the hazardous organics mentioned in the EPA""s drinking water rules.
The present invention recovers potable water from engine exhaust by manually or automatically diverting a desired portion of the exhaust gas stream to the water recovery system. The exhaust gas is preferably first passed through the vehicle""s catalytic converter. The catalytic converter generally contains catalyst consisting of platinum metals, transition metals or mixtures and oxides deposited either on alumina extrusions or honeycomb-type monolithic supports. The catalytic converter needs to be at a certain temperature to completely oxidize the hydrocarbons present in the exhaust. This normally requires temperatures of from about 700xc2x0 to about 1200xc2x0 F.
The conditions of the catalytic converter are important to the quality of the produced exhaust condensate. They can significantly affect the amount of particulates and TOC in the condensate. It has been determined that the lifetime of the catalytic converter (for purposes of this invention) is preferably less than about 50,000 miles, more preferably less than about 40,000 miles to produce water with the lowest TOC.
Another important factor is the temperature inside the catalytic converter, which depends mainly on the operating conditions of the vehicle. At low speeds or low vehicle engine loads, the temperature in the exhaust is lower than about 500xc2x0 F., which is not sufficient for the catalytic converter to fully oxidize the hydrocarbons present in the exhaust. It is preferable that the temperature be at least about 500xc2x0 F., preferably at least about 600xc2x0 F., or more preferably at least about 700xc2x0 F. in order to produce exhaust condensates with as low TOC as possible. In order to produce the highest quality drinking water, the exhaust gases are passed through the catalytic converter and vented through a bypass valve when the temperature in the catalytic converter is below the desired operating range. When the temperature of the catalytic converter reaches its operating range, the bypass valve is closed and the treated exhaust gas flows through the catalytic converter to the water collection unit.
The first part of the water collection unit is heat exchange. The heat exchangers used in the present invention can be manufactured from aluminum coated with Heresite, stainless steel (SS), inconel, ceramics, or graphite, preferably stainless steel, inconel or ceramic. The initial cooling generally takes place in either an air to gas heat exchanger or a counter-current gas to gas heat exchanger. For the air-gas heat exchange system, the exhaust gas is cooled to about 20xc2x0 F. above ambient temperature. The exhaust may then be further cooled in an air conditioner cooled condenser. In the most likely application scenario, the ambient xe2x80x9cdesertxe2x80x9d temperature is above the exhaust gas dew-point. Thus, ambient air cooling alone will be insufficient to condense any water at all. A source of cooler heat exchange fluid is required and this is most conveniently provided by refrigerant at 30-80xc2x0 F., or more preferably 30-50xc2x0 F., from a typical automotive air-conditioning system. The non-condensable gases from the exhaust are vented and the condensed water is pumped or passed by gravity through a particle filter, activated carbon filer and ion exchange resin column for removal of acidic, metallic, inorganic and remaining organic components and is then sent to a storage tank where it can be disinfected if storage is required for prolonged periods of time. Optionally, a small amount of sodium bicarbonate may be added to the water before carbon or ion exchange filtration. This buffers the water, raising its pH so that it will not attack the filters, particularly the ion exchange resins. It may also improve the taste of the water.
Key issues in putting together the water recovery system is the design of a system which fits in a standard vehicle and does not reduce significantly the efficiency of the engine, the removal of particulates and dissolved contaminants which affect taste and odor and can be hazardous to human health, the production of a high enough volume of water to be competitive with alternatives (e.g., carrying a large volume of water), and the ability to work in the high temperature and acidic environment of the exhaust system.
The present invention addresses these issues and will be more fully understood from the following detailed description of the invention.